If there's a relay to control the fan motor, then that's the problem.
Sometimes the control is solid state, but in any case, that's where the
problem is.


"AC/DCdude17" wrote in message
.. .
I've a gas furnace of unknown make, model and have an AC installed as
well. It connects to a thermostat through a four wire configuration.
The whole setup is about 13 years old. The thermostat have three settings
like the average thermostat. A/C(Red, yellow and green shorted),
heat(red, white and green shorted) and there's a switch labeled auto/on
that let's you turn on the blower manually(red and green shorted).

Every once in a while, furnace blower keeps running after turning off
after using fan only and only when I use fan only. I thought it was a
problem in the thermostat, so I pulled it out of the socket. Fan
continued to whir.

I measured the voltage across green and red and read 24V as the fan
continued to run, so it's clear that there isn't a short in control
wiring.

To shut it off, I'll have to short red and green a few times with a
paperclip at the thermostat socket and fan eventually turns off.

If I don't do this, it contiues to run forever. I can also do the same
shorting technique to get the blower stuck running. My assumption is that
pulsating the control terminals turns it off by jiggling the stuck
terminals apart.

Is there anything I should suspect beside the mechanical relay?

"AC/DCdude17" wrote in message
.. .
I've a gas furnace of unknown make, model and have an AC installed as
well. It connects to a thermostat through a four wire configuration.
The whole setup is about 13 years old. The thermostat have three settings
like the average thermostat. A/C(Red, yellow and green shorted),
heat(red, white and green shorted) and there's a switch labeled auto/on
that let's you turn on the blower manually(red and green shorted).

Every once in a while, furnace blower keeps running after turning off
after using fan only and only when I use fan only. I thought it was a
problem in the thermostat, so I pulled it out of the socket. Fan
continued to whir.

I measured the voltage across green and red and read 24V as the fan
continued to run, so it's clear that there isn't a short in control
wiring.

To shut it off, I'll have to short red and green a few times with a
paperclip at the thermostat socket and fan eventually turns off.

If I don't do this, it contiues to run forever. I can also do the same
shorting technique to get the blower stuck running. My assumption is that
pulsating the control terminals turns it off by jiggling the stuck
terminals apart.

Is there anything I should suspect beside the mechanical relay?

You should suspect that we can't tell you anything about your system without
seeing it. Make/model/serial numbers help, but still not enough information.
You shou should also suspect that you will find a local, *competent*,
licensed, professionally trained, HVAC technician in your Yellow Pages.

Could be a couple of things. You need a meter. If no meter call a tech.

TAB Dude

"TAB Dude" wrote in message
...
You need a meter. If no meter call a tech.

TAB Dude

In favor of the OP.

Read the post again.........he measured the 24v across the stat wires.
So, I believe he'd have to have a meter. :-)


--
kjpro
_-~-__-~-__-~-__-~-__-~-__-~-__-~-__-~-__-~-__-~-__-~-_

( kjpro @ starband . net ) remove spaces to e-mail

Want it done yesterday? Or done right today, to save money tomorrow!!

_________________________ __

Your right... A Good multi meter. The conditions you describe is indeed a
control issue, but most likely not your t-stat. you will need a meter that
will do milli amps. At best you will isolate the fault, see a burnt contact
and say "Oh!". More likely you will narrow the problem down to two possible
issues. At this point you will call atech or change parts. If you have a
$10.00 analoge meter from Sears, it will not do. Happy hunting!

TAB Dude

"AC/DCdude17" wrote in message
.. .

..Clueless garbage about an unknown unit snipped.


Is there anything I should suspect beside the mechanical relay?

Let your fingers do the walking and locate someone in your area that knows
what in hell he is doing?

"AC/DCdude17" wrote in message
.. .

..Clueless garbage about an unknown unit snipped.


Is there anything I should suspect beside the mechanical relay?

Let your fingers do the walking and locate someone in your area that knows
what in hell he is doing?

Your right... A Good multi meter. The conditions you describe is indeed a
control issue, but most likely not your t-stat. you will need a meter that
will do milli amps. At best you will isolate the fault, see a burnt contact
and say "Oh!". More likely you will narrow the problem down to two possible
issues. At this point you will call atech or change parts. If you have a
$10.00 analoge meter from Sears, it will not do. Happy hunting!

TAB Dude

"TAB Dude" wrote in message
...
You need a meter. If no meter call a tech.

TAB Dude

In favor of the OP.

Read the post again.........he measured the 24v across the stat wires.
So, I believe he'd have to have a meter. :-)


--
kjpro
_-~-__-~-__-~-__-~-__-~-__-~-__-~-__-~-__-~-__-~-__-~-_

( kjpro @ starband . net ) remove spaces to e-mail

Want it done yesterday? Or done right today, to save money tomorrow!!

_________________________ __

Could be a couple of things. You need a meter. If no meter call a tech.

TAB Dude

"AC/DCdude17" wrote in message
.. .
I've a gas furnace of unknown make, model and have an AC installed as
well. It connects to a thermostat through a four wire configuration.
The whole setup is about 13 years old. The thermostat have three settings
like the average thermostat. A/C(Red, yellow and green shorted),
heat(red, white and green shorted) and there's a switch labeled auto/on
that let's you turn on the blower manually(red and green shorted).

Every once in a while, furnace blower keeps running after turning off
after using fan only and only when I use fan only. I thought it was a
problem in the thermostat, so I pulled it out of the socket. Fan
continued to whir.

I measured the voltage across green and red and read 24V as the fan
continued to run, so it's clear that there isn't a short in control
wiring.

To shut it off, I'll have to short red and green a few times with a
paperclip at the thermostat socket and fan eventually turns off.

If I don't do this, it contiues to run forever. I can also do the same
shorting technique to get the blower stuck running. My assumption is that
pulsating the control terminals turns it off by jiggling the stuck
terminals apart.

Is there anything I should suspect beside the mechanical relay?

You should suspect that we can't tell you anything about your system without
seeing it. Make/model/serial numbers help, but still not enough information.
You shou should also suspect that you will find a local, *competent*,
licensed, professionally trained, HVAC technician in your Yellow Pages.